Propose single wrapping type

[JoviDeCroock]

This reduces the new AST-nodes to only be for the newly introduced type, this does make it so that when we invoke print we have to rely on the user to either specify that we're in semantic nullability mode or we could do a pre-traverse and when we enter a node with semantic-non-null we toggle it on ourselves.

The main reasoning behind removing the new name for our existing null type is that I would prefer to be backwards compatible in terms of schema structure. This because it might become complex for people to reason about composed schemas, i.e. a lot of individually parsed schemas that later on compose into a larger one.

I know that technically this is covered because in the classic ones we'll have the non wrapped null type and in the modern ones we'll have the semantic nullable wrapped type. For schema-builders like pothos and others I think this is rather complex to reason about and to supply us with. I would instead choose to absorb this complexity in the feature and stay backwards compatible.

This also sets us up for the SDL not being a breaking change, we only add one AST-type, what's left now is to settle on a semantic non-null syntax and making everything backwards compatible.

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